Field of the Invention
The present invention relates to epoxy coatings. The present invention particularly relates to curing agents for epoxy coatings.
Background of the Art
Historically, epoxy coatings are well known in the art for many end-use applications. One component necessary to preparing an epoxy coating is a curing agent. The curing agent is the component which is employed to render precursor resins into hardened coatings, often by pushing to completion the reaction of residual reactive species.
Typical commercially available waterborne curing agents based on polymeric adducts of polyamines with an epoxy resin have an amine hydrogen equivalent weight (AHEW), based on solids, of greater than 105. The consequence of this is that it requires high amine loadings in the coating formulation. Typical curing agent loadings are 1:1 to 4:1 epoxy:amine loading ratio (by weight) to form these coatings. The high amine loading ratio is necessary to achieve the appropriate equivalent ratio of epoxy to amine in the formulation in order to achieve proper cure of the coating by the adducts.
Further, a large amount of curing agent, typically at least 25% of the epoxy component weight, is required when grinding the pigmented side of a coatings formulation with the amine, in order to achieve adequate wetting of the pigment during the grind. High amine loadings result in greater hydrophilicity in the cured coating network due to the presence of high amounts of amine nitrogen and other hydrophilic components in the curing agent composition, leading to reduced corrosion resistance and greater water penetration. It would be desirable in the art to provide curing agents with low AHEW, which would allow for low amine loading in the hardenable film forming composition, resulting in lower hydrophilicity and improved corrosion resistance, as well as less color transfer from the curing agent to the cured film.
The low loading of the amine would also contribute to less blushing in a clear formulation, particularly for curing agents with primary amine nitrogen groups. It would be desirable in the art to provide curing agents which allow adequate pigment wetting at low loading levels when grinding the pigmented side of a paint formulation. The low amine loading would further offer a cost advantage, due to decreased demand for the curing agent component. There is a need for low color amine curing agents, which offer advantages in paint formulations which are color sensitive. There is a need for reduced cycle time of curing agent preparation, primarily for reduction in fixed costs during manufacture.